Abstract

False target (reverberation, clutter, etc.) detection is suppressed in an echo ranging system (sonar or radar) in which target velocity and range are measured using a composite Doppler invariant-like signal having at least two segments, such as are present in a "rooftop" or "vee" HFM signal, such composite signal having an ambiguity function with two or more ridge lines of different slopes that intersect along the zero-velocity time axis. A bank of matched filters provides a distribution of outputs which has an ambiguity function-like character with intersecting pairs of ridge lines, the intersecting points of said pairs characterizing the range and velocity of the echo returns. This distribution is adjusted so that the intersecting ridge lines of each pair have equal and opposite slopes with respect to the time axis. In particular, fixed reverberators, which would have ridge lines intersecting on the zero-velocity time axis, would be symmetrical about this axis. A target with velocity v would present ridge lines intersecting along the v-velocity time axis and be symmetrical about that axis. Thus, the reverberation and the moving target would each have crossed ridge lines whose characteristic intersecting patterns would each exhibit symmetries, but about separate and distinct axes. False targets, including clutter and reverberation, are suppressed by subtracting from the adjusted output distribution, a replica thereof, folded (rotated) 180° about a time axis containing the intersection of the ridge line pair corresponding to the false target which is to be suppressed. The rotation and subtraction of the replica from the adjusted distribution provides a set of outputs from which the real target velocity and range can be determined. The rotation-subtraction process can be implemented on an on-going basis to suppress a plurality or continuum of false targets and to achieve a desired width of a Doppler notch covering an arbitrary range of velocities.